Reminds me very much of Flow Free: iOS: https://itunes.apple.com/us/app/flow-free/id526641427 Android: https://play.google.com/store/apps/details?id=com.bigduckgam...

Incidentally, it would be nice if you could backtrack to remove colored path blocks if you make a mistake like accidentally dragging across a small corner. I've only tried the webapp version, so not sure if that works in the iOS one.